Early- and late-onset bipolar illness.

We categorized a sample of 134 bipolar probands into early- and late-onset groups; age 30 years was the cutting point. Early-onset probands had three times the morbidity risk /MR) for affective disorder in first-degree relatives as late-onset probands and a greater proportion of relatives with the more severe, bipolar form. Early-onset patients also exhibited more neuropsychological dysfunction, less frequently had a unipolar manic course, and had a greater MR for alcoholism in first-degree relatives. The two groups did not differ in other clinical or historical characteristics or in the proportion of EEG abnormalities. Age at illness onset is useful in clarifying the genetic basis of affective disorder. The data are consistent with a polygenic or multifactorial model of illness in which the more severe genotype is expressed earlier in life and through the course of illness.